Many medical devices worn on the body are powered by battery. In this regard, there are at least two kinds of batteries used for this purpose: “primary batteries” and “secondary batteries”. Primary batteries are generally not constructed or intended to be rechargeable, while secondary batteries are rechargeable. When the capacity of the battery begins to flag, it must be replaced or recharged. But, not all batteries can be recharged without adverse effects. When the power capacity of a primary battery falls below a certain level, it must be replaced. However, a secondary battery may have its capacity restored multiple times by recharging.
Typically, hearing aids are powered by primary batteries that require frequent replacement and are very small and difficult for children or elderly people to handle and replace. Other hearing aids are powered by secondary batteries that require frequent recharging. If a patient forgets to recharge the batteries during a convenient time, such as while sleeping, he may have to go without the hearing aid while the batteries are being recharged.